Conventionally, various backlight units that supply light to a liquid crystal display panel (non-light emitting type display panel) of a liquid crystal display device are developed. As an example of a backlight unit, there is a side-light type backlight unit described in a patent document 1. This backlight unit, as shown in a plan view of FIG. 3A, receives light from a LED (Light Emitting Diode) 112 via a side surface 141S of a light guide plate 141; and emits the light from a top surface 141U (here, a board on which the LED 112 is mounted is called a mount board 111).
And, in this backlight unit, to prevent light-amount unevenness (brightness unevenness) from occurring in the emitted light, the side surface 141S of the light guide plate 141 is formed into a saw-tooth shape; especially, a vertical angle is suitably designed (see FIG. 3B that is an enlarged view of FIG. 3A). According to this, the light from the LED 112 (light emitting element) efficiently enters the light guide plate 141, so that brightness unevenness becomes unlikely to occur.
Patent document 1: JP-A-2006-302710